Backlighting system for display screen

ABSTRACT

A circuit board on which the electronic components providing power to a series of light sources is positioned as near as possible to light sources in order to minimize parasitic energy losses which would be introduced by lengths of wiring. The light sources are usually elongate tubular Cold Cathode Fluorescent Tubes arranged parallel to one another in a single plane and the circuit board may be mounted directly over the light sources, towards one end of the tubes. Standard PCB board-to-board connectors may be provided at an edge of the circuit board and a further circuit board provided with a series of conductive tracks may provide both a mechanical and electrical connection between the circuit board and the light sources. A power distribution method is also disclosed in which both current and temperature of the light sources are monitored and regulated in order to extend the lifetime of the light sources and to stabilize their brightness.

RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 10/714,400, filed Nov. 17, 2003, which is now U.S.Pat. No. 7,095,180.

TECHNICAL FIELD

This invention relates to display apparatus and in particular, thoughnot solely, to the backlighting system employed in display apparatussuch as LCD display screens, more particularly, multi-layer display(MLD) screens.

BACKGROUND ART

Certain types of display apparatus, such as Liquid Crystal Display (LCD)screens used as computer screens or television screens, requirebacklighting in order to make display elements on the screen visible, ormore easily visible, to a viewer of the display unit.

Existing “flat” screen display units, for example LCD display screens,may be single-layer display (SLD) units having a single display layer orsingle planar array of liquid crystal pixels, or multi-layer display(MLD) units in which a number of planar arrays of LCD pixels are alignedin a stacked or sandwiched arrangement. Multi-layered display (MLD)units provide a significant improvement over existing single layerdisplay (SLD) units or displays. MLD units may be used to nest displaycontent over spacially displaced or stacked layers to provide anenhanced mechanism for information absorption and analysis by users. Anexample of an existing multi-layer display is discussed for example inWO9942889A.

Existing MLD units require a significant amount of light to illuminateimages on the foreground layer (closest to the viewer) through theprevious or lower layers. Often cold cathode fluorescent lamps (CCFT)are used to provide the backlight in SLD and MLD LCD display units andthese require supporting circuitry to generate an initial high startingvoltage and a subsequent lower maintenance voltage once the lamps are insustained discharge mode. This support circuitry and the tubes generateexcess heat within the display apparatus and due to the proximity of thepower supply wires required, power is wasted through currents producedas a result of parasitic capacitive coupling. These problems result in aneed to provide a relatively high capacity and quality power supply inexisting backlit display apparatus and often also results in the need toincorporate cooling components to remove the excess heat produced.

In CCFT lamps, ultra-violet (UV) light is produced via an electricaldischarge passing through Argon and Mercury vapour in the lamp. The UVlight reacts with a phosphor coating on the inside of the glass lampwhich converts the UV light to visible light. The phosphor blenddetermines the spectral content of the visible light produced by thelamp.

A high voltage is required to initiate the self-sustaining electricaldischarge through the gas vapour and, once started, a lower voltage isrequired to keep the discharge going. Power is supplied to the lampthrough a ballast capacitor which ensures that the power supply sees thelamp as a linear electrical load. The total luminous flux produced bythe lamp is dependent on the magnitude of the current through the lampand the cold spot temperature of the lamp. The optimal temperature rangefor the lamp is between about 45 and 55° C. while the optimal currentrange is between about 5 and 7 mA. If the temperature and/or current areoutside these ranges then the light output and life of the lamp willdecrease.

MLD units have many more lamps than SLD units. For example, an MLD unitmay have between 24 and 27 lamps. Conventionally, wires are used toattach an inverter to a lamp (or set of lamps) to its power supply. Twowires are required per lamp which results in a large number of wireswhich is cumbersome, messy, produces excessive ElectromagneticInterference (EMI) and results in power loss through the above mentionedcapacitive coupling, particularly in MLD units because of the increasednumber of lamps.

U.S. Pat. No. 6,326,738B discloses a backlighting system for an SLD unitin which the ballast capacitor is mounted on the circuit board substrateto which one end of the lamp is connected, thereby reducing the numberof wires required. This system allows two wires to be used to supplypower to all of the lamps in a backlighting system but results in brightand dark spots and variance as power can not be regulated easily toensure that each lamp receives the same amount of power. Power is alsolost in this system due to the introduced parasitic capacitance betweenthe supply wires and the metallic enclosure which is required.Furthermore, the system disclosed requires higher rated electroniccomponents such as inverters which are physically larger and moreexpensive.

It is therefore an object of the present invention to provide abacklighting system which goes at least some way towards overcoming theabove disadvantages or which will at least provide the public with auseful choice.

All references, including any patents or patent applications cited inthis specification are hereby incorporated by reference. No admission ismade that any reference constitutes prior art. The discussion of thereferences states what their authors assert, and the applicants reservethe right to challenge the accuracy and pertinency of the citeddocuments. It will be clearly understood that, although a number ofprior art publications are referred to herein, this reference does notconstitute an admission that any of these documents form part of thecommon general knowledge in the art, in New Zealand or in any othercountry.

It is acknowledged that the term ‘comprise’ may, under varyingjurisdictions, be attributed with either an exclusive or an inclusivemeaning. For the purpose of this specification, and unless otherwisenoted, the term ‘comprise’ shall have an inclusive meaning—i.e. that itwill be taken to mean an inclusion of not only the listed components itdirectly references, but also other non-specified components orelements. This rationale will also be used when the term ‘comprised’ or‘comprising’ is used in relation to one or more steps in a method orprocess.

DISCLOSURE OF INVENTION

Accordingly, in a first aspect, the invention consists in a backlightingsystem for a display apparatus comprising:

-   -   at least one light source,    -   electronic componentry adapted to receive electrical power and        to control the distribution of electrical power to the at least        one light source,    -   first and second circuit board substrate on which the electronic        componentry is mounted and including an arrangement of        conductive tracks, and    -   electrical connection means provided in the circuit board        substrate and connected to said conductive tracks,    -   wherein said electrical connection means is directly        electrically and physically connected to the at least one light        source to conduct said electrical power distributed by the        electronic componentry to said at least one light source, and    -   further electrical connection means are provided between said        first and second circuit board substrates.

Preferably, the light source is provided substantially in a displayplane and the first circuit board substrate is substantially planar andpositioned over the at least one light source substantially parallelwith the display plane.

Preferably, the second circuit board substrate is arranged substantiallyperpendicularly to the plane of the first circuit board substrate andthe display plane.

Preferably, said at least one light source comprises a plurality oftubular light sources having proximal and distal ends, the tubular lightsources aligned in a row and substantially in the same plane as thefirst circuit board substrate, the distal ends of the plurality oftubular light sources connected together and to a ground connection ofthe electronic componentry and the proximal ends connected to receiveelectrical power from the electronic componentry through the electricalconnection means.

Preferably, said first circuit board substrate includes at least onesubstantially straight edge adjacent to which said further electricalconnection means is provided, the further electrical connection meansincluding mechanical connection means provided on the first circuitboard substrate along the substantially straight edge and includingconductive pin means providing at least part of said further electricalconnection means.

Preferably, said mechanical connection means comprise standard board toboard connectors.

Preferably, said electronic componentry includes a plurality of controlmeans, each of which control the distribution of power to more than onelight source, each control means receiving feedback of the electricalpower consumption of its selected number of light sources and adjustingthe power supplied to the selected number of light sources accordingly.

Preferably, the electronic componentry includes inverters, each controlmeans controls more than one inverter and each inverter powers more thanone light source.

Preferably, a cooling means is also provided wherein said control meansalso receives feedback on a temperature within the display apparatus andadjusts the amount of cooling provided to at least said selected numberof light sources by said cooling means accordingly.

Preferably, the display apparatus is a multi-layer display.

In a further aspect, the invention consists in a power distributionsystem for at least one light source within a display apparatus whereina control means controls the distribution of power to the at least onelight source by carrying out the steps of:

-   -   i) detecting the electrical power consumed by the at least one        light source,    -   ii) determining whether the electrical power consumed by the at        least one light source is within predetermined limits,    -   iii) regulating the electrical power supplied to the at least        one light source based upon the detected power consumption to        maintain or return the power consumed by the at least one light        source between said predetermined limits, and    -   iv) repeating steps (i) to (iv).

Preferably, the step of regulating the electrical power supplied to theat least one light source comprises providing the light source with afirst light source brightness controlling power signal and a secondlight source current controlling power signal.

Preferably, said display apparatus includes a plurality of controlmeans, each of which are connected to an associated inverter to controlthe power distributed to more than one fluorescent light source, whereina capacitor associated with each fluorescent light source and itsassociated inverter.

Preferably, the power consumed by the at least one light source isdetermined by sensing the current through the at least one light source.

Preferably, said display apparatus also includes a temperature sensorwhich provides said control means with an indication of the temperaturein the vicinity of the at least one light source and the control meansalso carries out the steps of:

-   -   iia) determining whether the temperature of the at least one        light source is within predetermined limits, and    -   iiia) adjusting the power supplied to the at least one light        source based upon the temperature indication to maintain or        return the temperature of the at least one light source between        said predetermined limits.

Preferably, the display apparatus also includes cooling means adapted toprovide variable cooling to the at least one light source, wherein thecontrol means also carries out the step of:

-   -   iiib) controlling the electrical power supplied to the cooling        means based upon the temperature indication to maintain or        return the temperature of the at least one light source between        said predetermined limits.

Preferably, the respective steps of regulating and adjusting theelectrical power supplied to the at least one light source and the stepof controlling the power supplied to the cooling means occur by pulsewidth modulating the current or voltage supplied to the at least onelight source or the cooling means respectively.

Preferably, the pulse width modulation frequency employed in the step ofregulating the power supplied to the at least one light source isgreater than the pulse width modulation frequency employed in the stepof adjusting the power supplied to the at least one light source.

Preferably, the pulse width modulation frequency employed in the step ofregulating the power supplied to the at least one light source issufficiently high that the current supplied to the at least one lightsource, after being filtered by the inverter, is at a substantiallyconstant analogue or DC level.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from thefollowing description which is given by way of example only and withreference to the accompanying drawings in which:

FIG. 1 a is a perspective view of the backlighting system for a displayapparatus in accordance with a preferred embodiment of the presentinvention;

FIG. 1 b is a perspective view of a prior-art backlighting system for adisplay apparatus;

FIG. 2 a is a basic schematic block diagram of a circuit layout of theelectronic components associated with a single controller and inverterused in the backlighting system shown in FIG. 1 a;

FIG. 2 b is a basic schematic block diagram of a circuit layout of theelectronic components associated with a single controller and associatedinverter used in a prior-art backlighting system;

FIG. 3 is a basic schematic block diagram of a circuit layout of theelectronic components, including all of the inverters and controllersused in the backlighting system of FIG. 1 a;

FIG. 4 a is a flow diagram showing the main steps and decisions involvedin the operation of the power distribution/control system for thebacklighting system of FIG. 1;

FIG. 4 b is a flow diagram showing the steps and decisions involved inthe “Update fan LF PWM Control” step of the flow diagram of FIG. 4 a;

FIG. 4 c is a flow diagram showing the steps and decisions involved inthe “Update backlight HF PWM Control” step of the flow diagram of FIG. 4a;

FIG. 5 a is a basic schematic block diagram of a portion of the circuitlayout shown in FIG. 2 a illustrating the types of electrical signalsexisting at various parts of the circuit; and

FIG. 5 b is a series of waveform diagrams for some of the electricalsignals in FIG. 5 a.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference initially to FIGS. 1 b and 2 b, examples of abacklighting system and basic circuit block diagram according to theprior-art for controlling the power distribution to a series of lightsources such as fluorescent lamps, and in particular Cold CathodeFluorescent Tubes (CCFT) or lamps, are shown. The prior-art backlightingsystem includes a regulator 1 which receives DC input power and controlsthe amount of this input power fed to a royer 2. The royer 2 convertsthe DC voltage output by regulator 1 to an AC voltage which is boostedby a transformer 3. Commonly, the combination of royer and transformeris known as an inverter.

A ballast capacitor 4 is positioned between the secondary side of thetransformer and one end of the or each lamp 5 and is required in orderto establish a starting voltage and make the lamp appear as a linearelectrical load to the regulator/royer combination. Regulator 1 enablesthe backlighting system to regulate or control the brightness of thelamp and receives feedback of the current through the lamp from acurrent sense resistor 6. Regulator 1 typically has a very simplecontrol algorithm such as inverse proportional control wherein thereciprocal of the feedback signal is subtracted from the regulatorinput. An external microcontroller 7 receives user input (such asbrightness and contrast changes) from controls 8 and provides controlsignals to the regulator 1 in order to adjust the current supplied tothe lamp 5.

It can be seen that the majority of the electronic components aremounted on a circuit board substrate or printed circuit board (PCB) 9although inverters 2,3 are shown mounted separately from the PCB 9. Thelamps 5 are all mounted with their longitudinal axes parallel to oneanother and in the same plane. A first lamp-end circuit board 10 whichmay include the ballast capacitors 4 connects together the proximal endsof various of the lamps and a second lamp-end circuit board 11 connectstogether all of the distal ends of the lamps to ground wire 19. In FIG.1 b, half of the lamps receive power from a first inverter 2,3 while theother half of the lamps receive power from a second inverter 2,3.However, further inverters could be used to individually supply a largernumber of groups of lamps and this would result in a larger number ofwires running between inverters and lamp ends.

The lamp arrangement need not be a parallel series of tubular lamps. Thelamps may be generally tubular but “bent” into, for example, generally“S” or “W” type planar shapes in a similar way to Neon sign writing. Itwill be understood that a single “S” shaped planar lamp may replace thespace occupied by three straight tubular lamps but will require a thirdof the associated electronic componentry. A planar generally “S” shapedlamp will therefore produce less heat and will start and finish atdifferent tube end circuit boards 10,11. In contrast, a planar generally“W” shaped lamp will replace the space occupied by four straight tubularlamps but require a quarter of the electronic componentry. Generallyhowever, the arrangement of tubes will be substantially planar (in adisplay plane) to minimise the thickness of the display apparatus.

With reference now to FIGS. 1 a and 2 a, in accordance with a preferredembodiment of the present invention, a circuit board substrate or PCB 14is provided for mounting each of the electrical components forming thepower supply for the lamps 5. It can be seen that the PCB 14 ispreferably mounted over the lamps, substantially parallel to the planeof the lamps. The wires shown in FIG. 1 b have been removed and instead,contact means such as, for example short mechanical connection meanssuch as standard PCB board-to-board connectors 12, each having aplurality of relatively short and substantially inflexible protrudinglinks or conductive pins 13 are provided on PCB 14 which directlycontact lamp end circuit board 10. The board-to-board connectors 12 areprovided along a substantially straight edge of the PCB 14 and eachreceives the output from a respective ballast capacitor 4 mounted on PCB14. The proximal lamp-end circuit board 10 has been altered to receivethe conductive pins which are connected thereto and conductive tracksare provided on PCB 10 between the respective conductive pins 13 and therespective ends of a group of, for example four, lamps.

The length of links 13 between PCB 14 and the lamps is minimised toreduce parasitic power losses due to capacitive coupling. Usingboard-to-board connectors keeps the length of all the tracks between theinverters 2,3 and lamps 5 approximately the same so that the intensityof visible light produced by each of the lamps will be substantially thesame. As a result of the construction shown in FIG. 1 a, thebacklighting system according to the present invention is less bulky.The reduction in the number of wires which would otherwise be necessaryalso improves safety as the internal temperature in an MLD or SLD unitis elevated due to the number of light sources required. Furthermore,the serviceability of MLD or SLD units incorporating the presentinvention is improved as it is possible to replace the lamps all at onceby virtue of the inclusion of board-to-board connectors. The PCB 14 isalso of an improved mechanical shape (that is, wide and flat) incomparison to the board 9 of FIG. 1 b so heat conduction is improved asa result of a larger surface area. There is also no need for a person tomanually solder components in the backlighting system of the presentinvention as a machine can surface mount all of the components. Itshould be noted that the present invention is applicable to bothsingle-and multi-layer displays.

Alternatively in certain configurations the inverters 2,3 and lamps 5could be attached board to board without the need for connectors 12 withthe same advantages. That is, the PCB 14 and lamp-end board 10 could beintegrally provided, for example by forming PCB 14 in a substantially“L” shape to incorporate the function of circuit boards 10 and 14 orsubstantially “U” shape to incorporate the functionality of circuitboards 10, 11 and 14.

FIG. 2 a demonstrates the layout of electronic components within thebacklighting system's power supply for only one of the inverters 2,3according to a preferred embodiment of the present invention. It can beseen that the control means or microcontroller 7 now also incorporatesthe function of regulator 1. Preferably, controller 7 executespredetermined conditional steps or software (to be described below)stored in an associated storage device either within or associated withcontroller 7 and, in response to certain inputs, provides a modulated orpulsed or PWM output signal to a switch 15 which, in response, providesa modulated or pulsed or PWM input DC voltage signal (for example 12volts DC maximum) to royer 2 which effectively controls the brightnessof the lamp(s).

It can clearly be seen that a single inverter 2,3 in the layoutaccording to the present invention may provide power to more than onelamp 5 and that the voltage across the current sense resistor 6 providesan indication of the total current through all of the lamps in the groupconnected to that particular inverter 2,3. The position of the currentsense resistor could be moved from the distal ends of the lamps to, forexample, adjacent the secondary side of the transformer 3, in whichcase, it would be possible to reduce the length of the wires connectingthe controller 7 and the current sense resistor 6.

It can also be seen in FIG. 2 a that a cooling means such as a variablespeed fan 16 is also receives input from controller 7. The fan 16 isadapted to provide variable cooling to the lamps 5 which produce a largeamount of heat in use and the fan speed may be controlled, for example,by a PWM signal provided by the controller 7. A temperature sensor 17 isprovided in the vicinity of the lamps or a number of temperature sensorsare provided, one for each group of lamps, which provides a temperaturesignal indicative of a temperature within the display apparatus to thecontrollers or the controller associated with the particular group oflamps for which it is detecting the temperature. Other ambient sensorssuch as brightness may also be incorporated and provide feedback to thecontroller 7 which will adjust the power supplied to (and thereby thebrightness of) the lamp(s) accordingly.

With reference now to FIG. 3, it can be seen that in one embodiment ofthe present invention, three separate controllers 7 are provided, eachof which provides output control signals to two separate inverters 2,3and each inverter 2,3 provides a regulated voltage to four separatelamps. Input signals from a user (such as on/off and brightness andcontrast change requirements) are received via the user controls 8 andambient parameters such as temperature are provided to the controllers 7via sensors such as temperature sensor 17 while output control signalsare issued to external devices such as fan 16. Although switch 15 is notillustrated in FIG. 3, its function may still be incorporated.

The input signals may be communicated to each of the controllers via acommunication bus interconnecting all controllers and output signals toexternal devices (such as the fan 16) may be communicated directly via aparticular controller connected to that external device, or, one of thecontrollers (a “master” controller) may generate the output signal andthis may be transmitted via the communications bus 18 to a particular(“slave”) controller to which the external device is connected and thecontrol signal then passed to the external device from that slavecontroller. The communications bus 18 may be a single wire.

With reference to the flow diagrams of FIGS. 4 a, 4 b and 4 c, thecontrol algorithm or software executed by the or each controller inaccordance with a further aspect of the present invention will now bedescribed.

In FIG. 4 a, execution starts at block 20 and proceeds to the step ofinitialising the controller(s) or CPU(s) and then waits for an interruptto occur at block 28. The interrupt may be a user interrupt such as theuser providing input via an on./off switch or brightness or contrastadjustment input device in which case control passes to a series ofsteps starting with block 21 and the MLD unit is, for example turned offor on in blocks 22 and 23 respectively.

Alternatively, the interrupt may be timed or automatic and results inthe controller reading the temperature from sensor 17 at block 24. Ifthe temperature is greater than a predetermined maximum temperature thenthe MLD unit is turned off at block 25 to avoid damage to the unit.

In block 26 a decision is made as to whether the temperature is within apredetermined allowable or desirable temperature range. If thetemperature is not within that predetermined range then control passesto the flow chart of FIG. 4 b which will be described below in which thecooling provided by the fan and/or the brightness of the lamps areadjusted in order to bring the temperature back to within the allowablerange. If the temperature is found to be within the allowable range,then the lamp current is sensed via current sense resistor 6 at block27. Again, if the current is found to be above an absolute predeterminedmaximum current then the MLD unit is turned off at block 25 in order tominimise damage to the unit.

If the lamp current determined at block 27 is determined to be within adesired or allowable range (such as between 5 and 7 mA) then controlreturns to block 28 to wait for a further interrupt to occur. If howeverthe current is found to be outside the predetermined range then controlpasses to the flow diagram of FIG. 4 c in which lamp current isregulated as will be described further below.

As mentioned above, in order to commence the flow diagram of FIG. 4 b,the temperature sensor must have sensed a temperature outside the presetrange but less than the absolute maximum temperature. A decision is thenmade in block 30 as to whether the temperature is above the upper limitof the predetermined allowable range. If the temperature is above theupper limit, and the fan is currently turned off, then the fan is turnedon at a minimum PWM duty cycle in block 31 (the duty cycle may bedefined as the ON time divided by the sum of the ON time and OFF time inone cycle of the PWM waveform—100% duty cycle is fully on and 0% dutycycle is fully off). Control then returns to block 27 in the flowdiagram of FIG. 4 a.

If the temperature is above the upper limit and the fan is currently onand the current duty cycle of the PWM control signal to the fan is belowa predetermined maximum, then the duty cycle is increased by apredetermined amount in block 32 to slightly increase the fan speed andits cooling effect and control returns to block 27 in the flow diagramof FIG. 4 a.

If the temperature is above the upper limit and the fan is currently onand the current duty cycle of the PWM control signal to the fan is atits predetermined maximum, then a decision is made in block 33 as towhether the lamp brightness is at a minimum. If the lamp brightness isnot at its minimum then the lamp brightness is incrementally reduced atblock 33 by reducing the duty cycle of a first PWM power signal outputby the controller(s). This first power signal is at a comparatively lowfrequency, for example 200 Hz. Given a constant lamp current, adjustmentof the duty cycle of this low frequency PWM signal regulates thebrightness of the lamp(s). Effectively, the low frequency PWM signalturns the lamp(s) on and off at a rate which the human visual system cannot detect and at a rate at which the electronic components can notsmooth or filter down to a constant analogue or DC level. Control thenreturns to block 27 in the flow diagram of FIG. 4 a.

If the fan is on, the duty cycle of the fan's PWM signal is at itsmaximum and the backlight brightness is at its minimum (that is, theduty cycle of the first PWM signal is at its minimum preset value), thencontrol returns to block 27 in the flow diagram of FIG. 4 a.

If at block 30 it is found that the temperature is less than or equal tothe upper temperature limit and the fan is turned off then controlreturns to block 27 in the flow diagram of FIG. 4 a.

If at block 30 it is found that the temperature is less than or equal tothe upper temperature limit and the fan is on and operating above itsminimum PWM duty cycle then the duty cycle of the fan's PWM signal isincrementally decreased at block 36 to reduce its speed and coolingeffect and control returns to block 27 in the flow diagram of FIG. 4 a.

If at block 30 it is found that the temperature is less than or equal tothe upper temperature limit and the fan is on and operating at itsminimum PWM duty cycle and the backlight brightness is below its maximum(that is, the duty cycle of the first PWM signal is at below its maximumpreset value) then the duty cycle of the low frequency PWM power signalis incrementally increased at block 34 to slightly increase thebrightness of the lamp and control then returns to block 27 in the flowdiagram of FIG. 4 a.

If at block 30 it is found that the temperature is less than or equal tothe upper temperature limit and the fan is on and operating above itsminimum PWM duty cycle and the backlight brightness is at its maximumthen the fan is turned off at block 35 and control returns to block 27in the flow diagram of FIG. 4 a. This is the ideal operating situationin which the temperature of the lamp is within its range, the fan is offand the lamp is at its brightest.

As mentioned above, in order to commence the flow diagram of FIG. 4 c,the current sense resistor 6 must have sensed a lamp current outside thepreset range but less than the absolute maximum allowable current. Adecision is then made in block 40 as to whether the current is above theupper limit of the predetermined allowable range.

If the current is above the upper limit of the allowable range and theduty cycle of a second PWM power signal output by the controller(s) isabove a preset minimum duty cycle, then the duty cycle of this secondPWM power signal is incrementally decreased at block 41. This second PWMpower signal is at a comparatively high frequency, for example 50 kHzand directly regulates or determines the size of the lamp current.Because the frequency of this second PWM signal is relatively high, theelectronic components (such as capacitors and inductors) within thepower supply circuitry smooth or filter this signal to a constantanalogue or DC signal level. Accordingly, if the duty cycle of thissecond PWM power signal remains constant then a constant lamp currentwill flow and a constant lamp brightness will result which will in turnincrease the life of the lamp.

It will be noted at this point that the first and second PWM powersignals are separately generated but are applied to the inverter(s) 2,3in superposition.

If the lamp current is above the upper limit of the allowable range andthe second, high frequency PWM power signal is at its minimum dutycycle, then control returns to block 28 of FIG. 4 a to wait for afurther interrupt.

If the lamp current is found at block 40 to be less than or equal to theupper value of the allowable current range and the duty cycle of thehigh frequency PWM signal is not at its maximum preset value, then theduty cycle of the high frequency power signal is incrementally increasedand control then returns to block 28 of FIG. 4 a.

Finally, if the lamp current is found at block 40 to be less than orequal to the upper value of the allowable current range and the dutycycle of the high frequency PWM signal is at its maximum preset value,then control returns to block 28 of FIG. 4 a to wait for a furtherinterrupt.

The present invention, at least in its preferred form provides a numberof advantages over the prior art. The reduction of the number and lengthof wiring reduces the amount of power loss through EMI and capacitivecoupling and therefore allows the power rating of the power supply to bereduced or additional lamps to be added to the backlighting system. Thepositioning of the circuit board substrate in the present invention alsobeneficially minimises the footprint of the backlight system. Thecontrol algorithm of the controller in accordance with the presentinvention ensures that the power supplied to the various lamps withinthe backlighting system are balanced so that a consistent brightness ofthe display screen may be obtained across its entire surface area. Thecontrol algorithm also extends the operating life of the lamps bymaintaining their operating temperature and current within allowableparameters.

FIGS. 5 a and 5 b demonstrate the types and waveforms of electricalsignals at various positions throughout the electrical circuit in thepreferred embodiment of the present invention. In FIG. 5 a an additionalcircuit element of a DC input filter 2 a has been illustrated (althoughthis could form part of the inverter 2,3) which effectively smoothes orfilters the superposed low 52 and high 53 frequency PWM power signals.

FIG. 5 b illustrates the way in which the low 52 and high 53 frequencyPWM signals are combined and filtered. The duty cycle of the examplesignals 52 and 53 shown in FIG. 5 b is approximately 50% (that is,t_(ON)≈t_(OFF)). Preferably, the low and high frequency signals areeffectively logically ANDed together so that signal 50 is high only ifboth signals 52 and 53 are high at the same time. The output of switch15 is therefore a pulsed 12V DC signal consisting of high frequencypulses in a low frequency envelope having substantially the same shapedwaveform as signal 50.

Ripples 54 appear in waveform 51 as a result of the filtering orsmoothing of the high frequency component of the combined signal 50.Royer 2 converts waveform 51 to an AC signal 55, preferably withoutaltering its magnitude significantly. Transformer 3 then steps up the ACsignal to a higher voltage AC signal 56 for supply to the light source 5or sources of the display apparatus.

It should be noted that the present invention could incorporate lightsources other than CCFT lamps which require Energisation via an ACcurrent. For example, light sources in which the output brightness isdependent upon the magnitude of an AC or DC voltage could be utilised inwhich case it may not be necessary to provide inverters 2,3.

Aspects of the present invention have been described by way of exampleonly and it should be appreciated that modifications and additions maybe made thereto without departing from the scope thereof.

1. A method of regulating power supplied to at least one light source,said method comprising: measuring current associated with said at leastone light source; and regulating said power supplied to said at leastone light source based upon said measured current, wherein saidregulating said power further comprises regulating said power to said atleast one light source using a pulse-width modulated signal, whereinsaid pulse-width modulated signal comprises high frequency componentsassociated with regulation of said power, and wherein said pulse-widthmodulated signal further comprises low frequency components associatedwith an amount of said power supplied to said at least one light source.2. The method of claim 1, wherein said pulse-width modulated signal isselected from a group consisting of a pulse-width modulated currentsignal and a pulse-width modulated voltage signal.
 3. The method ofclaim 1, wherein said regulating is performed by a processor.
 4. Themethod of claim 3, wherein said current associated with said at leastone light source is measured by a current measurement component, andwherein a signal representing said measured current is generated by saidcurrent measurement component and fed back to said processor forperforming said regulating.
 5. The method of claim 1, wherein said atleast one light source is operable to provide backlight for a display.6. The method of claim 1, wherein said regulating is performed by afirst processor and a second processor, wherein said first processor isoperable to regulate power supplied to a first light source, and whereinsaid second processor is operable to regulate power supplied to a secondlight source.
 7. The method of claim 6, wherein said first processor isoperable to control said second processor.
 8. The method of claim 6,wherein said first processor is coupled to said second processor by aninterface, and wherein said first and second processors are operable toaccess input signals from said interface.
 9. The method of claim 1further comprising: measuring a temperature associated with said atleast one light source; and adjusting said power supplied to said atleast one light source based upon said temperature.
 10. The method ofclaim 1 further comprising: measuring a temperature associated with saidat least one light source; and controlling the speed of a fan forcooling said at least one light source based upon said temperature. 11.The method of claim 1 further comprising: accessing a user input signal;and adjusting said pulse-width modulated signal based said user inputsignal.
 12. The method of claim 11, wherein said user input signalcomprises a request for a change in an attribute associated with said atleast one light source, and wherein said attribute is selected from agroup consisting of a power status, a brightness and a contrast.
 13. Themethod of claim 11, wherein said user input signal comprises a requestfor a change in an attribute associated with said at least one lightsource, and wherein said attribute is selected from a group consistingof a power status, a brightness and a contrast.
 14. The method of claim1 further comprising: generating a pulse-width modulated DC signal fromsaid pulse-width modulated signal; and inverting said pulse-widthmodulated DC signal to generate an AC signal for powering said at leastone light source.
 15. A system for regulating power supplied to at leastone light source, said system comprising: a current measurementcomponent for measuring current associated with said at least one lightsource; and a processor for regulating said power supplied to said atleast one light source using a pulse-width modulated signal, whereinsaid regulating is based upon a current measurement signal generated bysaid current measurement component and accessed by said processor,wherein said pulse-width modulated signal comprises high frequencycomponents associated with regulation of said power, and wherein saidpulse-width modulated signal further comprises low frequency componentsassociated with an amount of said power supplied to said at least onelight source.
 16. The system of claim 15, wherein said pulse-widthmodulated signal is selected from a group consisting of a pulse-widthmodulated current signal and a pulse-width modulated voltage signal. 17.The system of claim 15, wherein said at least one light source isoperable to provide backlight for a display.
 18. The system of claim 15further comprising: a temperature measurement component for measuring atemperature associated with said at least one light source.
 19. Thesystem of claim 18, wherein said processor is operable to adjust saidpower supplied to said at least one light source based upon saidtemperature.
 20. The system of claim 18, wherein said processor isoperable to control the speed of a fan for cooling said at least onelight source based upon said temperature.
 21. The system of claim 15,wherein said processor is operable to adjust said pulse-width modulatedsignal based on a user input signal accessed by said processor.
 22. Thesystem of claim 21, wherein said user input signal comprises a requestfor a change in an attribute associated with said at least one lightsource, and wherein said attribute is selected from a group consistingof a power status, a brightness and a contrast.
 23. The system of claim15 further comprising: a component coupled to said processor and forgenerating a pulse-width modulated DC signal from said pulse-widthmodulated signal; and an inverter coupled to said component and forinverting said pulse-width modulated DC signal to generate an AC signalfor powering said at least one light source.
 24. A system comprising: afirst current measurement component for measuring current associatedwith a first light source; a second current measurement component formeasuring current associated with a second light source; a firstprocessor for regulating power supplied to said first light source usinga first pulse-width modulated signal, wherein said regulating by saidfirst processor is based upon a first current measurement signalgenerated by said first current measurement component and accessed bysaid first processor; and a second processor for regulating powersupplied to said second light source using a second pulse-widthmodulated signal, wherein said regulating by said second processor isbased upon a second current measurement signal generated by said secondcurrent measurement component and accessed by said second processor. 25.The system of claim 24, wherein said first processor is operable tocontrol said second processor.
 26. The system of claim 24 furthercomprising: an interface coupling said first processor to said secondprocessor, wherein said first and second processors are operable toaccess input signals from said interface.
 27. The system of claim 24,wherein said first and second pulse-width modulated signals are selectedfrom a group consisting of a pulse-width modulated current signal and apulse-width modulated voltage signal.
 28. The system of claim 24,wherein said first and second pulse-width modulated signals comprisehigh frequency components associated with regulation of said power tosaid respective light sources, and wherein said first and secondpulse-width modulated signals further comprise low frequency componentsassociated with an amount of said power supplied to said respectivelight sources.
 29. The system of claim 24, wherein said first and secondlight sources are operable to provide backlight for a display.
 30. Thesystem of claim 24 further comprising: a temperature measurementcomponent for measuring a temperature associated with a light sourceselected from a group consisting of said first and second light sources.31. The system of claim 30, wherein at least one processor selected froma group consisting of said first and second processors is operable toadjust said power supplied to said respective light sources based uponsaid temperature.
 32. The system of claim 30, wherein at least oneprocessor selected from a group consisting of said first and secondprocessors is operable to control the speed of a fan for cooling said atleast one light source based upon said temperature.
 33. The system ofclaim 24, wherein at least one processor selected from a groupconsisting of said first and second processors is operable to adjustsaid respective pulse-width modulated signals based on a user inputsignal accessed by at least one processor selected from a groupconsisting of said first and second processors.
 34. The system of claim33, wherein said user input signal comprises a request for a change inan attribute associated with at least one light source selected from agroup consisting of said first and second light sources, and whereinsaid attribute is selected from a group consisting of a power status, abrightness and a contrast.
 35. The system of claim 24 furthercomprising: a first component coupled to said first processor and forgenerating a first pulse-width modulated DC signal from said firstpulse-width modulated signal; a first inverter coupled to said firstcomponent and for inverting said first pulse-width modulated DC signalto generate a first AC signal for powering said first light source; asecond component coupled to said second processor and for generating asecond pulse-width modulated DC signal from said second pulse-widthmodulated signal; and a second inverter coupled to said second componentand for inverting said second pulse-width modulated DC signal togenerate a second AC signal for powering said second light source.
 36. Amethod of regulating power supplied to at least one light source, saidmethod comprising: measuring current associated with said at least onelight source; and regulating said power supplied to said at least onelight source using a pulse-width modulated signal, wherein saidregulating is based upon said measured current, wherein said regulatingfurther comprises regulating said power using a first processor and asecond processor, wherein said first processor is operable to regulatepower supplied to a first light source, and wherein said secondprocessor is operable to regulate power supplied to a second lightsource.
 37. The method of claim 36, wherein said pulse-width modulatedsignal is selected from a group consisting of a pulse-width modulatedcurrent signal and a pulse-width modulated voltage signal.
 38. Themethod of claim 36, wherein said pulse-width modulated signal compriseshigh frequency components associated with regulation of said power, andwherein said pulse-width modulated signal further comprises lowfrequency components associated with an amount of said power supplied tosaid at least one light source.
 39. The method of claim 36, wherein saidregulating is performed by a processor.
 40. The method of claim 39,wherein said current associated with said at least one light source ismeasured by a current measurement component, and wherein a signalrepresenting said measured current is generated by said currentmeasurement component and fed back to said processor for performing saidregulating.
 41. The method of claim 36, wherein said at least one lightsource is operable to provide backlight for a display.
 42. The method ofclaim 36, wherein said first processor is operable to control saidsecond processor.
 43. The method of claim 36, wherein said firstprocessor is coupled to said second processor by an interface, andwherein said first and second processors are operable to access inputsignals from said interface.
 44. The method of claim 36 furthercomprising: measuring a temperature associated with said at least onelight source; and adjusting said power supplied to said at least onelight source based upon said temperature.
 45. The method of claim 36further comprising: measuring a temperature associated with said atleast one light source; and controlling the speed of a fan for coolingsaid at least one light source based upon said temperature.
 46. Themethod of claim 36 further comprising: accessing a user input signal;and adjusting said pulse-width modulated signal based said user inputsignal.
 47. The method of claim 46, wherein said user input signalcomprises a request for a change in an attribute associated with said atleast one light source, and wherein said attribute is selected from agroup consisting of a power status, a brightness and a contrast.
 48. Themethod of claim 36 further comprising: generating a pulse-widthmodulated DC signal from said pulse-width modulated signal; andinverting said pulse-width modulated DC signal to generate an AC signalfor powering said at least one light source.
 49. A method of regulatingpower supplied to at least one light source, said method comprising:measuring current associated with said at least one light source;regulating said power supplied to said at least one light source using apulse-width modulated signal, wherein said regulating is based upon saidmeasured current; measuring a temperature associated with said at leastone light source; and controlling the speed of a fan for cooling said atleast one light source based upon said temperature.
 50. The method ofclaim 49, wherein said pulse-width modulated signal is selected from agroup consisting of a pulse-width modulated current signal and apulse-width modulated voltage signal.
 51. The method of claim 49,wherein said pulse-width modulated signal comprises high frequencycomponents associated with regulation of said power, and wherein saidpulse-width modulated signal further comprises low frequency componentsassociated with an amount of said power supplied to said at least onelight source.
 52. The method of claim 49, wherein said regulating isperformed by a processor.
 53. The method of claim 52, wherein saidcurrent associated with said at least one light source is measured by acurrent measurement component, and wherein a signal representing saidmeasured current is generated by said current measurement component andfed back to said processor for performing said regulating.
 54. Themethod of claim 49, wherein said at least one light source is operableto provide backlight for a display.
 55. The method of claim 49, whereinsaid regulating is performed by a first processor and a secondprocessor, wherein said first processor is operable to regulate powersupplied to a first light source, and wherein said second processor isoperable to regulate power supplied to a second light source.
 56. Themethod of claim 55, wherein said first processor is operable to controlsaid second processor.
 57. The method of claim 55, wherein said firstprocessor is coupled to said second processor by an interface, andwherein said first and second processors are operable to access inputsignals from said interface.
 58. The method of claim 49 furthercomprising: adjusting said power supplied to said at least one lightsource based upon said temperature.
 59. The method of claim 49 furthercomprising: accessing a user input signal; and adjusting saidpulse-width modulated signal based said user input signal.
 60. Themethod of claim 49 further comprising: generating a pulse-widthmodulated DC signal from said pulse-width modulated signal; andinverting said pulse-width modulated DC signal to generate an AC signalfor powering said at least one light source.
 61. A system for regulatingpower supplied to at least one light source, said system comprising: acurrent measurement component for measuring current associated with saidat least one light source; a temperature measurement component formeasuring a temperature associated with said at least one light source;and a processor for regulating said power supplied to said at least onelight source using a pulse-width modulated signal, wherein saidregulating is based upon a current measurement signal generated by saidcurrent measurement component and accessed by said processor, andwherein said processor is further operable to control the speed of a fanfor cooling said at least one light source based upon said temperature.62. The system of claim 61, wherein said pulse-width modulated signal isselected from a group consisting of a pulse-width modulated currentsignal and a pulse-width modulated voltage signal.
 63. The system ofclaim 61, wherein said pulse-width modulated signal comprises highfrequency components associated with regulation of said power, andwherein said pulse-width modulated signal further comprises lowfrequency components associated with an amount of said power supplied tosaid at least one light source.
 64. The system of claim 61, wherein saidat least one light source is operable to provide backlight for adisplay.
 65. The system of claim 61, wherein said processor is operableto adjust said power supplied to said at least one light source basedupon said temperature.
 66. The system of claim 61, wherein saidprocessor is operable to adjust said pulse-width modulated signal basedon a user input signal accessed by said processor.
 67. The system ofclaim 66, wherein said user input signal comprises a request for achange in an attribute associated with said at least one light source,and wherein said attribute is selected from a group consisting of apower status, a brightness and a contrast.
 68. The system of claim 61further comprising: a component coupled to said processor and forgenerating a pulse-width modulated DC signal from said pulse-widthmodulated signal; and an inverter coupled to said component and forinverting said pulse-width modulated DC signal to generate an AC signalfor powering said at least one light source.